Immunity, breastfeeding, and the timing of measles vaccine

The Pediatric Insider

© 2015 Roy Benaroch, MD

Leave it to Disney to make a splash—any day now, we’ll hear that Anna and Elsa have caught the measles themselves (imagine a link to the sisters all covered with spots, looking miserable in the hospital, with a worried snowman and moose cowering in the background. “For the first time in forever… measles is back….”)

I’ve already covered the outbreak in detail. Briefly: over the December holiday someone at one of Disneyland’s theme parks in California brought in measles. At least 5 employees and probably about 40 park visitors caught it, almost all of whom were unvaccinated. Since then, despite a massive public health effort to identify and isolate potentially infectious contacts, the outbreak has spread to about 100 cases in 6 states. Again, and this can’t be repeated too much, almost all of the cases are occurring in people who have not been fully vaccinated, either because they’re babies who are too young, or for other reasons. It’s not yet clear exactly what that breakdown is. Some of the cases could have and should have been vaccinated; it’s likely that others had health issues that prevented timely vaccination. In any case, since measles is super-contagious, it will likely continue to spread, especially among communities with poor immunization coverage. Sadly, this has been an entirely predictable and avoidable outbreak.

A few comments and notes sent in—thanks especially Emily and Jennifer–have asked for more details about the MMR vaccine and how immunity affects how it works. I feel another Q&A coming on….


Aren’t newborns pretty well protected against measles, from mom’s antibodies?

The placenta sends lots of important things to baby—oxygen, nutrition, growth factors, love, and what’s called “passive immunity” via maternal antibodies. These are large molecules, a kind of immunoglobulin called “IgG” which mom had made previously after exposures to diseases or vaccines. Good maternal immunity to things like influenza and measles does provide good protection for their newborns. That’s why it’s important for pregnant women to get flu vaccines, and for all girls to get all of their vaccines—so later, when they’re pregnant, their little babies get protection, too.

But those IgGs from momma, they don’t last so long. The “titers” drop off fairly rapidly, and the protection falls quickly. Best protection probably lasts weeks, with some protection falling off over months. By six months of age, there’s probably no protection from maternal IgGs.

However, there’s still some small amount of IgGs circulating. Though they’re not protective, they can interfere with some kinds of vaccines (especially live, attenuated vaccines like MMR and chicken pox.) That’s why these vaccines are ordinarily given at 12 months of life or later. It’s not dangerous to give them early—it’s just that they probably won’t work as well to provide strong, lasting protection. Maternal IgGs do not interfere with the effectiveness of many other vaccines, like the Hepatitis B, DTaP, polio, and the other vaccines given in the first year of life.


Can you give MMR vaccine earlier, say if exposure risk is high?

Yes, though it may not work as well or provide protection that’s long-lasting. Current recommendations are to give the first dose of MMR routinely at 12-15 months of life. It should be given early (as early as 6 months) if the risk of exposure is high. For example, the CDC currently recommends early MMR for international travel to Europe, Asia, the Pacific, and Africa. I think it would also be prudent to vaccinate early for travel to California, especially if your baby will be in crowded places like airports or theme parks (California officials have said that these places are safe—IF you’re vaccinated.)

A dose of MMR vaccine given in the 6 – 11 month window will provide some protection, but since the lingering maternal IgGs will prevent it from being fully effective the dose doesn’t “count.” Two further doses will still be needed, following the typical schedule at 12-15 months and at 4-5 years of age.


Doesn’t breastfeeding give baby antibodies? Wouldn’t that prevent measles? Or can breastfeeding interfere with the MMR vaccine?

Breastmilk does contain antibodies, but they’re a different kind of antibodies. They’re not the IgG antibodies that circulate in the blood, they’re IgA antibodies that concentrate more in body secretions, including nasal mucus and breast milk. These IgA molecules don’t interfere with vaccines. They provide modest protection against mostly gastrointestinal infections (think diarrhea and vomiting illnesses)—which makes sense, because the breastmilk IgA molecules are swallowed. They don’t make their way into the blood, or at least not very much—like other proteins, if you swallow them they’re mostly torn apart during digestion. Breastmilk IgA provides just a little protection against infections that are caught via the respiratory tract, including the common cold and measles. For instance, a breastfed baby on average statistically will likely get one half of an ear infection fewer in the first year of life. Not a huge impact, at least not in respect to those kinds of infections.


Is there any way to test for those maternal measles IgG antibodies? I mean, if my baby’s antibodies are low enough at 9 months of age, could I get him vaccinated then?

Well, you can test for them, but the exact amount doesn’t perfectly correlate with whether the baby will become immune after the vaccine. You won’t know if the vaccine given at 9 months worked well unless you test your baby afterwards—and even then, there’s a grey zone in the measurements.


Maybe we should test for immunity? I mean, should we be testing children after the MMR to make sure it worked?

After one dose of MMR, about 85% of children will get complete, lifelong protection against the three components: measles, mumps, and rubella. The second dose, traditionally given at age 4-5, will pick up almost all of the remaining unprotected 15%, leaving only 1% non-immune. Those odds are really, really good—and if a community has high vaccination rates, that 1% of kids whose MMR didn’t take are still well protected by herd immunity. Of course, if vaccine rates fall, it all falls apart. The 1% who didn’t respond are vulnerable, as are babies too young to vaccinate and people with health conditions that preclude vaccination.

Testing for immunity can done under special circumstances, sometimes to help control an outbreak, or in people at risk for losing immunity after chemotherapy, for instance. But the testing is expensive and kind of a hassle (it’s not always easy to draw blood from children, and they don’t like it very much.) Because the vaccine is so safe, it makes more sense to just give the two doses than to test everyone.

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23 Comments on “Immunity, breastfeeding, and the timing of measles vaccine”

  1. lilady Says:

    Thank you for this very complete explanation about maternal passive immunity. I’ve seen a bunch of comments from non vaccinating mothers who believe that breast feeding protects their babies from measles and pertussis.


  2. reissd Says:

    Thank you, this is really really helpful.


  3. Jennifer Says:

    Thank you so very much for posting this, which clearly and succinctly answers all of my questions.


  4. Dr. Roy Says:

    lilady, you’re right– I’m not one to discourage breastfeeding, but in truth the passive IgAs are minimally protective against respiratory transmission of infections. Which makes sense, when you remember that they only work where they are: in the mouth and in the gut. Not in the nose, not on the conjunctiva, not in the lungs, not in the blood. We’re often too meek to point out the (often well-intentioned) exaggerations of the benefits of breast milk.


  5. lilady Says:

    Breast feed your baby because you want to…not because you have the mistaken belief that you are protecting your baby in lieu of vaccines.

    I’m a proponent of breast feeding and I’m strongly pro-vaccine and I’m not too meek to post comments on blogs to encourage moms to follow the AAP Recommended Childhood Vaccine Schedule.

    Dr. Roy, the 2015 Recommended Childhood Vaccine Schedule now has the 6-12 month MMR vaccine recommendation for travel to measles endemic areas of the world:

    Click to access 0-18yrs-schedule.pdf


  6. Dr. Roy Says:

    Thx– glad to see “early MMR” made into into the official PDF thing. It’s been part of CDC statements for a while. I wonder if they’ll officially add “California” as an endemic area?


  7. lilady Says:

    When public health staff in California and Disneyland spokespersons are cautioning parents whose children are not up-to-date, or are younger than age one, to have their youngsters get MMR vaccine, you know the outbreak is serious.


  8. Dr. M Says:

    Love this post! Sharing everywhere commences now.


  9. Shannon Says:

    Thanks for a great article. What are your thoughts for parents of infants? Should we get an MMR booster/update?


  10. Dr. Roy Says:

    Shannon, parents who’ve had two doses of MMR should have about 99% protection, which really is very good. I don’t think an extra dose beyond that would be warranted. But if you’re not sure if you’ve gotten two doses, getting an “extra” dose won’t hurt.

    In the past, only one dose was recommended– after one dose, protection is probably in the 85% range. The specific guidelines on adults needing one versus two doses are a little confusing– to me, it makes more sense to just get the second dose. If you’re curious about the details, they’re covered in this post:


  11. Caroline McCormic Says:

    If a six month old infant is going to be traveling to a place that could have measles, is it safe to get the early dose of MMR on the same day the baby gets his usual six month vaccines (and he gets these shots on the day exactly six months from his birth)? I hope this makes sense, and thanks in advance!


  12. Dr. Roy Says:

    Caroline, a first dose of MMR can be given as early as 6 months. It can be given on the same day as all other ordinary 6 month vaccines. BUT (and I know this is confusing!) — if not given on SAME DAY, it shouldn’t be given in a 28 day window after the 6 month dose of rotavirus vaccine.

    A dose of MMR given earlier than 12 months is only for short term protection for travel to a risky area. It will not “count” later as one of the two doses for lifelong immunity. For long term protection, TWO doses of MMR are required. The first can be given as early as 12 months, and the second 28 or more days later (typically, the second dose is given at age 4. More about that soon!)


  13. Says:

    Thanks so much for your response! I have read so much conflicting information on this, and I appreciate your easy to understand explanation.:)


  14. Jenna Says:

    Dr. Roy,
    I have a related question about giving the mmr vaccine to kids under 1 year. How long after receiving the vaccine is a child considered to have the immunity?


  15. Dr. Roy Says:

    Jenna, immunity to measles is probably established within 5-10 days after a dose of MMR. Mumps takes longer, more in the range of 3 weeks.


  16. Caroline Says:

    Hi, I have another question. I have read some studies that say that infants who receive an early shot of MMR don’t respond as well to getting the 12 month and 4-6 year MMR shots, leaving them more are risk for the rest of their lives than they would have been if they hadn’t gotten the early MMR. I have read other studies that said while the early MMR doesn’t work as well as the MMR does after the first birthday, it helps to prime the immune system to respond very well to the later MMRs, making the MMR work even better. What are your thoughts on this?


  17. Dr. Roy Says:

    Caroline, it’s complicated. There are actually two somewhat-independent ways that MMR vaccines confer immunity, called the “humoral” response (that’s antibodies) and the “cell-mediated” response. An early MMR may blunt the humoral response to later MMRs (meaning antibody levels will be lower), but even though they’re lower they’re typically still protective. And early vaccination may actually help the body develop a more-robust “cell mediated” type of immunity. In practice, children who get an early dose < 12 mos followed by two standard doses at 12-15 months and 4-5 years have excellent protection in the range of 99%, which is in practice the same protection as children who didn't get that early dose.


  18. Caroline Says:

    I had been confused by what I read, and I really appreciate you explaining it. 🙂 There is a possibility we are going to need to get our son an early MMR, and I was worried it would leave him unprotected later. I am very glad to find out that he should still be protected after the two regular mmr shots.


  19. MB Says:

    Would there be a good reason to seek the second dose of the MMR ahead of schedule, on the assumption that the child is up-to-date with his vaccines?


  20. Dr. Roy Says:

    MB, the second dose increases immunity from ~ 95% to ~ 99%. So though one dose is pretty darn good, two doses are better. That second dose doesn’t have to wait until age 4, it can be given any time 28 days or more after the 1st for full effect.

    I think an early second dose would be especially a good idea for children heading out of the country, or to California.

    Note that as of right now, there has not been any change in the official recommendations for timing of MMR. I’m just discussing a change within the “wiggle room” of the current guidelines.


  21. typesandy@aol.coml Says:

    How would you feel about flying with a three month old breastfed child in light of the measles outbreak?


  22. Dr. Roy Says:

    Typically maternal IgG antibodies from across the placenta during pregnancy convey good protection for the first six months of life (assuming mom was immunized.) That “six month” isn’t a guarantee, but at three months your baby is likely protected. I would consider where the current hot spots are (right now, Ukraine, and some other parts of Europe) in making travel plans for everybody.


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